Ferrous and non-ferrous surfaced articles may suffer surface deterioration by corrosion through contact with the atmosphere or moisture, or both. Chemical passivation treatments are widely used to inhibit or suppress such surface corrosion.
One of the passivating treatments employed for this purpose consists in treating the ferrous or non-ferrous surface with an aqueous solution of phosphoric acid or its salt. Various types of chromic acid compositions have also been used.
While phosphate and chromic acid based passivating solutions have been widely adopted, they have been by no means effective in preventing corrosion under all conditions, especially where the treated surface is further coated with a synthetic resin coating composition which dries to form a synthetic resinous film. Excellent results have been obtained in the use of chromic acid-containing compositions as described, for example, in U.S. Pat. No. 4,266,988. However, due to environmental considerations, there is a need to provide a passivating treatment for ferrous and non-ferrous metal surfaced articles which eliminates a requirement for chromium compounds while at the same time providing a passivating treatment wherein the ferrous or non-ferrous metal surface is receptive to a synthetic resinous coating composition. This need is particularly important in processes where a synthetic resinous coating composition such as a primer-type paint is electrodeposited from a large electrodeposition bath, which bath in due course may involve a disposal problem in which the presence of chromium compounds would complicate the solution to the problem.
An object of this invention is to provide a treatment for ferrous and non-ferrous metal coated articles so as to passivate the surfaces of said articles and make them receptive to synthetic resinous films, especially when such films are electro-deposited, without requiring the use of a chromium compound.
Another object of the invention is to provide a process in which a ferrous or non-ferrous metal such as, for example, cold rolled steel, galvanized steel and aluminum having a zinc phosphate, iron phosphate or manganese-iron phosphate surface is given a rinse with a non-chromium containing solution which acts as a chemical binding agent so as to passivate the final surface and provide better corrosion resistance.